Linear density gradients of bovine serum albumin will be utilized to separate the heterogeneous leukemit cell types. The leukemic cell types to be studied will be following: AKR mice, BALB/C mice, C3H mice and human monocytic, lymphocytic, granulocytic and plasmacytic. The cells in the separated fractions will be characterized using the light microscope, scanning and transmission microscope, histochemistry, cell volume and tritiated thymindine uptake. Chemotherapeutic agents will be administered to mice and humans and the selective destruction will be measured by observing the shift of cells in the density gradients. It is anticipated that the dormant drug resistant cell will be isolated and characterized and identified by these techniques. The cells in various fractions before and after therapy will be assayed in vivo for leukemic cells to normal AKR mice.